NUMERICAL-SIMULATION OF NONLINEAR IONIZATION NONUNIFORMITIES IN NONEQUILIBRIUM DISK MHD GENERATOR

The formation and evolution of the ionization nonuniformities from ini tial disturbances of amplitude in the nonequilibrium Ar-Cs plasma in m agnetohydrodynamic (MHD) generator is studied by the numerical simulat ion, The simulations are carried out in the wide interval of electron temperatures corresponding to the region at which the seed partially i onizes, the region of the linear plasma stability at the fully ionized seed, and the region of the instability corresponding to the partial ionization of Ar at high electron temperatures, Initial disturbances o f finite amplitude in electron temperature and density are introduced at the time t = 0 into the homogeneous plasma distribution, and the cr itical amplitudes determining the development of the instability are c alculated, The initial disturbances are constructed using random funct ions with different spatial scales, The results are compared with the calculation of the critical amplitudes from the nonlinear theory of th e plane ionization waves, It is found that at electron temperatures lo wer than 5500 K, the temperature dependence of the critical amplitudes and the structure of the nonlinear waves agree well with the nonlinea r theory, In the electron temperature region corresponding to the part ial ionization of the noble gas (T-e > 5500 K), the finite ionization rate of argon atoms is essential for analysis of the instability, In t his region the margin of the plasma stability is wider than it is pred icted by the nonlinear theory, The nonuniformity in the argon ion numb er density plays the dominating role in the instability development at high electron temperatures (T-e > 5500 K) in comparison with the nonu niformity in T-e in the initial disturbances.